Method and apparatus for studying particles having widely different sizes

ABSTRACT

An apparatus for studying particles of widely different sizes includes a vessel and a fluid medium in the vessel with the particles suspended thereon. First and second aperture tubes are suspended in the vessel at a first height, and a third aperture tube is suspended at a second lower height. The first aperture tube has an aperture of substantially smaller size than the second and third aperture tubes. The rate of entry through the aperture and into the second tube, of particles large enough to cause blockage of the first aperture in the first tube, is detected. When this rate drops below a first particular rate, indicating that substantially all particles greater than that size have settled below this particular height in the beaker, control circuitry is actuated to enable the fluid to enter into the first tube via the aperture therein for analyzing particles received therein via Coulter type detectors. Control circuitry may also be initiated to allow fluid to enter the third tube through its aperture for analyzing the particles received therein via Coulter type detectors.

United States Patent [191 Coulter et al.

[ 1 May 6,1975

Walter R. Hogg, Miami Lakes, both of Fla.

[73] Assignee: Coulter Electronics, Inc., Hialeah,

Fla.

[22] Filed: Feb. 6, 1974 [21] Appl. No.: 439,875

[52] U.S. Cl. 324/71 CP; 73/432 PS [51] Int. Cl. G01n 27/00 [58] Field of Search 324/71 CP; 73/432 PS [56] References Cited UNITED STATES PATENTS 5/1969 Coulter et al 324/71 CP 5/1969 Coulter et al 324/71 CP Primary Examiner-Alfred E. Smith Assistant Examiner-Rolf Hille Attorney, Agent, or FirmSilverman & Cass, Ltd.

[57] ABSTRACT An apparatus for studying particles of widely different sizes includes a vessel and a fluid medium in the vessel with the particles suspended thereon. First and second aperture tubes are suspended in the vessel at a first height, and a third aperture tube is suspended at a second lower height. The first aperture tube has an aperture of substantially smaller size than the second and third aperture tubes. The rate of entry through the aperture and into the second tube, of particles large enough to cause blockage of the first aperture in the first tube, is detected. When this rate drops below a first particular rate, indicating that substantially all particles greater than that size have settled below this particular height in the beaker, control circuitry is actuated to enable the fluid to enter into the first tube via the aperture therein for analyzing particles received therein via Coulter type detectors.

Control circuitry may also be initiated to allow fluid to enter the third tube through its aperture for analyzing the particles received therein via Coulter type detectors.

27 Claims, 2 Drawing Figures METHOD AND APPARATUS FOR STUDYING PARTICLES HAVING WIDELY DIFFERENT SIZES BACKGROUND OF THE INVENTION This invention relates generally to particle analyzing apparatus of the type on which particles suspended in a fluid medium are caused to move through an electric current path of small dimensions, and more particularly to a structure enabling use of such apparatus for studying particles having widely different sizes.

Now well known in the art are apparatus and techniques based upon the principles of operation pioneered by Wallace H. Coulter, one of the present inventors. According to the principles and techniques of Coulter, an electronic counting and sizing apparatus, hereinafter termed the Coulter type apparatus, is provided such as is claimed in and described in U.S. Pat. No. 2,656,508. The Coulter apparatus produces an electrical signal each time that a particle suspended in a fluid passes through an electric current path of small dimension, which, in the first commercial apparatus, is constricted by a minute aperture in a wall of insulating material disposed between two bodies of the fluid. The apparatus includes means for moving the fluid through the aperture to carry the particles along with the fluid; a source of electric current, electrodes immersed in the fluid on opposite sides 'of the wall and connected to the source of current providing a constricted current path between the electrodes and through the aperture, a detector connected to the electrodes and responsive to the changes in resistance or electrical impedance of the aperture contents each time that a particle passes therethrough to develop a detection signal, and some form of counter to respond to the signals detected.

In its various forms, the apparatus is known and sold throughout the world under the trademark Coulter Counter. The Coulter type apparatus will include means for moving the fluid, such as a syphon or manometer; means for metering the fluid such as a metering device of the type described in U.S. Pat. No. 2,869,078; means for containing the fluid such as vessels, beaker tubes, conduits and the like; means for coupling the current source and detector to the fluid, such as electrode systems and leads; and means for establishing a minute opening or aperture in the wall between bodies of fluid such as the aperture formed in a wafer or other member set into a wall of a glass tube immersed in a vessel of sample fluid. The aperture in effect scans the suspension passing through it and reference will be hereinafter made to the portion which produces the signals as a scanning system.

Since the amplitude of the signal generated by the passage of a particle through the aperture is proportional to the volume of the particle, the apparatus has been widely used for sizing as well as counting. Multiple apertures, however, must be employed if particles of widely varying sizes are to be counted and sized. This is because the use of a single aperture of a compromise diameter results in a decreased sensitivity of the aperture to the small particles, and the possibility of increased coincidence loss for a given particle concentration. It could also introduce an error in linear response to particles greater than or percent of the aperture diameter. Generally in such arrangements multiple dilutions are required to get the best results. It also required scalping or decanting to prevent blockages by large particles.

Various applications have been made utilizing multiple channels for obtaining statistical information on size distribution and for studying particles having widely different sizes. One such apparatus is described in U.S. Pat. No. 3,603,875. Such systems are particularly important in industrial systems wherein particle size and concentration must be determined for a vast gamut of materials such as, for example, slurries, dusts, powders, emulsions, and the like. Although the Coulter type apparatus has replaced Stokesian methods involving sedimentation, such apparatus has been somewhat troubled by aperture blockage in systems wherein the particles to be detected vary greatly in size. These problems have been recognized and a number of solutions have been implemented. For example, U.S. Pat. 3,259,842 describes a debris alarm which indicates the blockage of the aperture so as to allow the technician to clear the aperture blockage and reinstitute use of the apparatus. U.S. Pat. 3,444,463 describes a system wherein parallel samplings are taken so that one sampling may be discarded in the event the aperture becomes blocked.

In these and other related patents, the solution has always been to compensate after a blockage has occurred such as for example by voting out the sampling taken from the blocked aperture, or by statistically manipulating the data taken at the time of blockage in order to yield a reasonably correct result from the data obtained from the blocked aperture. The user in all cases is still presented with the problem of partially dismantling the apparatus in order to clear the blockage from the apparatus, or employing automatic equipment which is a part of the apparatus in order to remove the blocking particle from the aperture. These systems do not attempt to forestall blockage of an aperture of small dimensions by a particle of large dimensions.

SUMMARY OF THE INVENTION In practicing this invention an apparatus is provided for sizing and counting particles of widely differing sizes which uses the Coulter principle. The apparatus includes a first vessel carrying a body of fluid having particles suspended therein of widely varying size. First, second and thirdtubes, having first, second and third apertures therein respectively for enabling flow of fluid from the vessel into the tubes are positioned in the vessel. The first and second tubes are positioned at a first height in the vessel and the third tube is positioned at a second lower height in the vessel. The third aperture is large enough to accommodate the largest particle in the fluid suspension. The first aperture in the first tube is substantially smaller than the second and third apertures. First, second and third fluid control systems are coupled respectively to the first, second and third tubes for causing the fluid to flow from the vessel through the apertures into the tubes. An actuating device is provided for actuating the second and third fluid control systems for enabling flow of fluid through the second and third apertures. First, second and third scanning systems are provided and are coupled respectively to the first, second and third apertures. Each of the scanning systems is responsive to the passage of each particle through the aperture associated therewith to produce an electric signal the value of which is related to the dimensions of the particle. Threshold circuitry is coupled to the second scanning system and is operativein response to the reduction in the repetition rate of electric signals in excess of a particular value, indicating a reduction in the number of particles in excess of a particular size, to develop a control signal. The first fluid control system is operative in response to the control signal to enable flow of fluid from the vessel through the first aperture into the first tube. Signal analyzers are also provided and coupled to the scanning systems attached to the first and third tubes. The signal analyzers analyze the electric signals produced by the first and third scanning systems for providing indications of particle size and concentration.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a pictorial representation of the beaker and aperture tubes used in the apparatus of this invention;

FIG. 2 is a block diagram of the automatic circuitry used in the apparatus of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown a vessel which may be a simple beaker. Three tubes 22, 24, and 26 are partially immersed in a body of fluid 28. Tubes 22 and 24 are immersed to substantially the same depth beneath the surface of fluid 28, and tube 26 is immersed to a substantially greater depth than tubes 22 and 24. Tube 26, in the preferred embodiment, is positioned close to the bottom of beaker 20, and tubes 22 and 24 are positioned somewhat near the surface of fluid 28. Tubes 22, 24 and 26 are called aperture tubes because they each have microscopic apertures 32, 34, and 36 respectively therein. Aperture tube 22 has a small aperture 32, relatively speaking, whereas aperture tubes 24 and 26 have large apertures 34 and 36 relatively speaking. For example, aperture 32 can be 50 microns in diameter whereas apertures 34 and 36 can be 250 or even 500 microns in diameter. Although apertures 34 and 36 have a size ratio with respect to one another of as much as two to one, for purposes of this application, they are considered substantially the same in size.

Vessel 20, aperture tubes 22, 24 and 26, and fluid 28, constitute portions of a Coulter type particle analyzer such as is well known in the art. Such apparatus is shown and described in US. Pat. No. 2,656,508. Multiple aperture fittings, which may for example be employed for at least the aperture 22 and 24, are shown and described in US. Pat. No. 3,444,464; and a particle analyzing apparatus for use with the multiple aperture fittings is shown and described in US. Pat. No. 3,444,463.

Particles to be analyzed are suspended in fluid 28 which is poured into beaker 20. It is to be understood, of course, that the particles to be analyzed which are suspended in fluid 28 vary greatly in size. In any small increment of volume, such as 40, the particles entering the volume from above, will equal the particles leaving the volume from below, as long as the distribution of particle sizes is relatively uniform throughout fluid 28. However, as the large particles settle faster than the small and medium size particles a point in time will be reached when the large particles no longer enter volume 40 at the same rate from the top as they leave from the bottom. If the increment of volume 40 is located for example at the level of apertures 32 and 34, a point will be reached where there are no particles larger in size than the aperture 32, or large enough to block aperture 32. To digress for a moment, it should be understood that if for example aperture 32 is 30 microns in size, multiple or odd-shaped particles greater in size than 10 microns can cause blockage of aperture 32. It then will not be possible to block aperture 32. However, smaller particles of interest are still present at the height of the aperture 32 at this time and it is desired to analyze these particles.

In operation, the fluid 28, with particles to be analyzed suspended therein, is either allowed to flow through apertures 34 and 36 of aperture tubes 24 and 26, or is forced to so flow. As particles pass through aperture tubes 24 and 26, they will cause particle pulses to be developed, in accordance with the well known Coulter principle, having amplitudes proportional to the size of the particle passed through the aperture. Those pulses developed in response to passage of particles through aperture 36 will be at least counted. The rate at which pulses in excess of a particular amplitude, representing particles large enough to block aperture 32, are developed, in response to passage of particles through aperture 34, will be monitored. When the rate decreases below a predetermined point, thus indicating that statistically very few particles large enough to block aperture 32 are present at that height in fluid 28, circuitry will be activated to allow fluid 28 to flow through aperture 32 in aperture tube 22, or to force fluid 28 to so flow. That is, when the concentration of particles large enough to block aperture 32, and at or above the height of aperture 32, decreases below a con centration which will cause blockage of aperture 32, fluid 28 will be allowed to flow into aperture 32. Small particles suspended in fluid 28 can then be analyzed by passage through aperture 32, without fear of blocking aperture 32 by a larger particle.

Referring now to FIG. 2 which is the block diagram of the apparatus, when fluid 28 in FIG. 1 has been entered into beaker 20 for a period of time sufficient to allow particles to begin to settle down through fluid 28, push button 44 can be depressed. Actuation of push button 44 causes actuation of control circuit 46. Control circuit 46 may, for example, be a device which changes state in response to actuation of push button 44 and develops a control voltage at conductor 48. This control voltage is coupled via conductor 48 to aperture fluid flow control 50, aperture current source 52, delay circuit 54, aperture fluid flow control 56, aperture current source 58 and delay circuit 60. Aperture fluid flow control 56 and aperture fluid flow control 50 in the preferred embodiment are suction devices attached to tubes 24 and 26 respectively. Some fluid flow control devices are illustrated in US. Pat. Nos. 2,869,078 No. 3,015,775. Fluid flow control devices 50 and 56 when actuated cause fluid 28 to flow from beaker 20 through apertures 34 and 36 of aperture tubes 24 and 26 respectively.

Aperture current source 52 and aperture current source 58 operate upon the above noted Coulter principle. Both include a source of power or power supply and two electrodes immersed in fluid 28. One of the two electrodes may be common to both aperture current source 52 and aperture current source 58. A second electrode for aperture current source 52 is positioned in aperture tube 24, and a second electrode for aperture current source 58 is positioned in aperture tube 26.

Aperture current source 52 and aperture current source 58 are coupled to control circuit 46 via conductor 48, and will be actuated in response to the control signal from the control circuit 46. When actuated they will develop a current path between the electrodes and through apertures 34 and 36 respectively. Particles passing through apertures 34 or 36 will cause modulation of the current paths in accordance with the now well known Coulter principle which in turn will cause a pulse to be developed whose amplitude is related to the size of the particle passing through the aperture. In FIG. 2, pulses developed in response to passage of a particle through aperture 34 are shown as being coupled from aperture 34 to amplifier 62, and pulse developed in response to particles passing through aperture 36 are shown as being coupled from aperture 36 to amplifier 64.

The control signal developed at conductor 48 by control circuit 46 is also coupled to delay circuits 54 and 60. Delay circuits 54 and 60 may, for example, consist of a monostable and trailing edge detector, coupled in series and operative in response to the control signal to develop a delay signal a predetermined period of time after the control signal. The purpose of delay circuits 54 and 60 is to provide a delay sufficient to allow aperture fluid flow controls 50 and 56 and aperture current sources 52 and 58 to reach an equilibrium condition or steady state. In another embodiment, delay circuits 54 and 60 would be contacts of a manometer syphon structure which would be part of aperture fluid flow controls 50 and 56. Such contacts are shown and described in US. Pat. No. 3,259,842. The delay signals developed by delay circuits 54 and 60 are coupled to bistable multivibrators 66 and 68 respectively. Bistable multivibrators 66 and 68 in the preferred embodiment are RS type flip-flops most commonly known in the art as RS flip-flops. The delay circuit signals are coupled to the set" inputs of flip-flops 66 and 68 causing them to change states and develop a logical one signal at their outputs. The logical one signals developed by flip-flops 66 and 68 are coupled to the control inputs of analog switches 70 and 72 respectively.

The delay signal developed by the delay circuit 60 is also coupled to volume measuring circuit 74. Volume measuring circuit 74 is operative in response to the delay circuit signal to begin measuring the volume of fluid 28 passing throuogh aperture 36 in aperture tube 26. When volume measuring circuit 74 has measured a predetermined volume of fluid 28 passing through aperture 36, it will develop a reset signal which is coupled to the reset input of the flip-flop 68 causing flip-flop 68 to reset and revert to its original state. With flip-flop in its original state, it will develop a logical zero at its output which is coupled to the control input analog switch 72. Volume measuring circuit 74 in one embodiment is a portion of aperture fluid flow control 56. In such a system, volume measuring circuit 74 would be a second contact of a manometer syphon structure which would be closed after a predetermined metered amount of fluid 28 has passed through aperture 36. Such a contact arrangement is also shown and described in US. Pat. No. 3,259,842.

Analog switch 72 operates such that when a logical one is coupled to its control input from flip-flop 68 it will couple the pulses developed in response to passage of particles through aperture 36, and amplified by amplifier 64, from amplifier 64 to pulse analyzer counter 76. Pulse analyzer counter 76 is of the type now well known in the art which will count each pulse.

Pulse analyzer counter 76 can also analyze certain characteristics of the pulse, such as for example, its amplitude and/or duration in order to ascertain certain characteristics of each particle detected, such as for example, the particle size and shape. It is to be understood that aperture 36 as noted above is quite a large aperture. As a consequence, particles passing through aperture 36 which are smaller than a predetermined percentage of the size of aperture 36, say for example 3 percent of the aperture size, will not adequately be sensed. Either a pulse will not be developed in response to passage of such particles through aperture 36, or the pulse will not have sufficient amplitude and duration to allow pulse analyzer/counter 74 to operate.

Analog switch is identical to analog switch 72 and operates such that when a logical one is coupled to its control input from flip-flop 66 it will couple the pulses, developed in response to particles passing through aperture 34, and amplified by amplifier 62, from amplifier 62 to threshold circuit 78. Threshold circuit 78 is operative only in response to pulses in ex cess of a predetermined amplitude to develope a threshold signal. The threshold amplitude of threshold circuit 78 is selected such that it is equal to an amplitude corresponding to a particle size which will block aperture 32 in aperture tube 22. The threshold signals developed by threshold circuit 78 are coupled through OR gate 79 to the reset input of integrator circuit 80.

A source of potential such as battery 82 is coupled to integrator circuit 80 through potentiometer 84. Integrator circuit 80 is operative in response to the current from battery 82 to develop an integration voltage. lntegrator circuit 80 will discharge this integration voltage in response to the threshold signal coupled to the reset input of integrator circuit 80 through or gate 79 from threshold circuit 78. In operation, then each time a particle which is large enough to block aperture 32 in aperture tube 22 passes through aperture 34 of aperture tube 24, threshold circuit 78 will develop a threshold signal which is coupled through OR gate 79 to integrator circuit 80 causing it to discharge the integration voltage developed. If the rate at which particles large enough to block aperture 32, and passing through aperture 34 decreases below a predetermined rate, thus indicating the relative absence of particles large enough to block aperture 32, integrator circuit 80 will not discharge often enough and will develop an integration voltage in excess of that necessary to actuate threshold circuit 86. Threshold circuit 86 will develop a threshold signal when the integration voltage developed by integrator citcuit 80 exceeds its threshold level which is coupled to an input of bistable 88. In the embodiment shown, bistable 88 is an RS flip-flop just as flip-flops 66 and 68, and threshold circuit 86 is coupled to the set" input. Flip-flop 88 is operative in response to the threshold signal coupled from threshold circuit 86 to develop a logical one which is coupled to delay circuit 92, aperture fluid flow control 94 and aperture current source 96.

A second output of flip-flop 66 is coupled to the reset input of integrator circuit 80 through a second input of OR gate 79. This second or not output develops a logical one when flip-flop 66 is reset or in a nonactivated state, and develops a logical zero when flipflop 66 is in its second state. That is, the not output will develop a logical one when the regular output develops a logical zero, and will develop a logical zero when the regular output develops a logical one. The connection to the reset input of integrator circuit 80 maintains integrator circuit 80 in a reset state until such time as aperture fluid flow control 50 and aperture current source 52 are actuated, stabilize, and fluid 28 is flowing through aperture 34 in a stable fashion so that particles can be detected.

Aperture fluid flow control 94 and aperture current source 96 are identical to aperture fluid flow control 56 and aperture current source 58. Aperture fluid flow control 94 will operate in response to the logical one coupled from flip-flop 88 to allow fluid 28 to flow through aperture 32 into aperture tube 22. Aperture current source 96 will operate in response to the logical one coupled from flip-flop 88 to develop a current path through aperture 32 in aperture tube 22. The passage of particles through aperture 32 will cause pulses to be developed, as described above with respect to the passage of particles through aperture 36, which are coupled to amplifier 98. Amplifier 98 amplifies the pulses and couples them to the input of analog switch 100.

Delay circuit 92 is identical in operation to delay circuit 60 previously described and will develop a delay signal a predetermined period of time after receipt of a logical one from flip-flop 88. The predetermined period of time is provided in order to allow aperture fluid flow control 94 and aperture current source 96 to reach an equilibrium condition. The delay signal is coupled to the set input of flip-flop 102 and to the input of volume measuring circuit 104. Flip-flop 102 will change states in response to the delay signal and develop a logical one at its output which is coupled to the control input of analog switch 100. Analog switch 100 is operative in response to the logical one coupled to the control input to allow the amplified pulses developed by amplifier 98 to be coupled to pulse analyzer 106 for counting and analysis of the pulses. It is to be understood again, that aperture 32 is much smaller than apertures 34 and 36 so that counting and analysis of the small particles suspended in fluid 28 can be accomplished simultaneously with counting and analysis of large particles via aperture 36 and pulse analyzed counter 76, and without fear of clogging or blocking aperture 32 by the presence of large particles.

Volume measuring circuit 104 is substantially the same as volume measuring circuit 74 and will operate in response to the delay signal from delay circuit 92 to begin measuring the volume of fluid 28 passing through aperture 32 in aperture tube 22. When a predetermined volume has been measured, volume measuring circuit 104 will develop a reset signal which is coupled to the reset input of flip-flops 102, 66 and 88 causing them to reset and revert to their original state. With flip-flop 102 reset a logical zero is coupled to the control input of analog switch 100, thus terminating the counting and analysis by pulse analyzer counter 106 of particles passing through aperture 32. The reset pulse coupled to flip-flop 88 will cause it to reset thus terminating further operation of aperture fluid flow countrol 94 and aperture current source 96. The reset signal coupled to flip-flop 66 will cause it to reset thus closing analog switch 70 and preventing pulses from being coupled from amplifier 62 to threshold circuit 78.

It is to be understood that further modifications and adaptations of the above noted circuitry are contemplated as being within the scope of this patent. For example, control circuit 46 can develop separate control signals for aperture fluid flow control 50 and aperture current source 52, delayed in time compared to the other control signals it develops. The delay allows the largest particles in fluid 28 to settle below the height of apertures 32 and 34. This allows use of an aperture 34 which is smaller than aperture 36, for example, by a ratio of two to one. Aperture 34 of course must still be substantially larger than aperture 32. Control circuit 46 may include an automatic reset which can be coupled to the output of volume measuring circuit 104. The signal developed by volume measuring circuit 104 when the appropriate volume of fluid 28 passing through aperture 32 has been measured can then be used to reset or terminate operation of the entire system. Furthermore, alternative arrangements for turning off all or part of the total system either simultaneously or sequentially can be envisioned so that the system is prepared to begin a new measurement cycle.

What it is desired to be secured by letters Patent of the United States is:

1. A method for studying particles of widely different sizes wherein the particles are suspended in a liquid medium in a vessel and settle through the medium from top to bottom at a rate determined by their size, said method including the steps of:

detecting the concentration at a particular height in said vessel of particles suspended in said liquid medium in excess of a particular size,

allowing the liquid medium and particles suspended therein to pass through a first aperture in a first tube positioned at said particular height in said vessel in response to said concentration at said particular height decreasing below a first detected concentration, and

allowing the liquid medium and particles suspended therein to pass into a second tube, at a second particular height on said beaker through a second aperture substantially greater in size than said first aperture.

2. The method of claim 1 further including the steps of:

detecting each particle suspended in said liquid medium passing into said first tube through said first aperture,

detecting each particle suspended in said liquid medium passing into said second tube through said second aperture.

3. The method of claim 2 wherein said step of detecting each particle passing into said first and second tubes includes the step of generating an electrical signal in response to passage through one of said first and second apertures of a particle suspended in said fluid medium, and processing said electrical signal to at least separately count said particles passing into said first and second tubes.

4. The method of claim 3 wherein the value of said electrical signal is related to the dimensions of the particle and further including the step of processing said electrical signal to determine said dimensions.

5. The method of claim 1 wherein said step of detecting the concentration includes,

allowing the liquid medium to pass through a third aperture substantially greater in size to said first aperture, detecting particles passing through said third aperture and greater in size than said particular size,

detecting a decrease in the rate of passage through said third aperture of particles in excess of said particular size.

6. The method of claim wherein the step of detecting said concentration includes the step of,

generating an electrical signal in response to passage through said third aperture of a particle greater in size than said particular size,

detecting the repetition rate of said electrical signals,

detecting a decrease in the repetition rate of said electrical signals below a predetermined repetition rate.

7. The method of claim 1 wherein the steps of allowing said liquid medium to pass includes the step of creating a pressure differential between said vessel and said first and second tubes for drawing said liquid through said first and second apertures.

8. The method of claim 7 wherein said step of creating a pressure differential includes the step of creating a vacuum in said first and second tubes.

9. An apparatus for studying particles of widely different sizes suspended in a fluid by passage of said fluid from a vessel to one of a plurality of tubes positioned in said vessel wherein each of said plurality of tubes has an aperture therein for passage of said fluid therethrough, said apparatus comprising,

at least a first and second of said plurality of tubes positioned at a first height in said vessel, said first tube having a first aperture of a first particular size therein and said second tube having a second aperture of a second particular size greater than said first particular size,

at least a third of said plurality of tubes at a second,

lower height in said vessel, said third tube having a third aperture therein substantially larger than said first particular size of said first aperture,

first control means for controlling passage of said fluid from said vessel to said first tube,

first sensing means coupled to said second tube and said first control means for sensing the rate of particles entering said second tube from said vessel through said second aperture, said first sensing means operative in response to a reduction in the rate of particles in excess of a particular size entering said second tube to actuate said control means for allowing fluid to flow from said vessel into said first tube, and

second control means for controlling passage of said fluid from said vessel to said third tube.

10. The apparatus of claim 9 further including third control means for controlling passage of said fluid from said vessel into said second tube.

11. The apparatus of claim 9 further including second sensing means coupled to said first aperture for sensing particles entering said first tube from said vessel through said first aperture.

12. The apparatus of claim 9 further including third sensing means coupled to said third aperture for sensing particles in said fluid entering said third tube through said third aperture from said vessel.

13. The apparatus of claim 9 wherein said first sensing means includes first scanning means coupled to said second tube and operative in response to passage of particles in said fluid through said second aperture to produce an electric signal for each passing particle the value of which is related to the dimensions of the respective particles, and threshold means coupled to said first scanning means and operative in response to a reduction in the repetition rate of said electric signals in excess of a particular value to develop a control signal, said control means being coupled to said threshold means and operative in response to said control signal to allow fluid to flow from said vessel to said first tube.

14. The apparatus of claim 11 wherein said second sensing means includes second scanning means coupled to said first aperture in said first tube and operative in response to passage of particles in said fluid through said first aperture to produce an electric signal for each passing particle the value of which is related to the dimensions of the respective particle, and processing means coupled to said second scanning means and operative in response to each of said electrical signals to at least count said signals for counting the number of particles passing into said first tube.

15. The apparatus of claim 12 wherein said third sensing means includes third scanning means coupled to said third aperture in said third tube and operative in response to passage of particles in said fluid through said third aperture to produce an electric signal for each passing particle the value of which is related to the dimensions of the respective particles, and processing means coupled to said third scanning means and operative in response to said electric signals to at least count said electric signals for counting the number of particles passing into said third tube.

16. The apparatus of claim 9 further including second control means coupled to said second tube for controlling passage of said fluid from said vessel to said second tube, and third control means coupled to said third tube for controlling passage of said fluid from said vessel to said third tube.

17. The apparatus of claim 16 further including second sensing means coupled to said first aperture for sensing particles entering said first tube from said vessel, and third sensing means coupled to said third aperture for sensing particles entering said third tube from said vessel.

18. The apparatus of claim 17 wherein said first sensing means includes first scanning means coupled to said second aperture in said second tube and operative in response to passage of particles through said aperture and into said second tube to produce an electric signal for each passing particle the value of which is related to the dimensions of the respective particle, and threshold means coupled to said first scanning means and operative in response to the reduction in the repetition rate of said electric signals in excess of a particular value to develop a control signal, said control means being coupled to said threshold means and operative in response to said control signal to allow fluid to flow from said vessel to said first tube.

19. The apparatus of claim 18 wherein saidsecond and third sensing means each include scanning means coupled to said apertures and operative in response to passage of particles through said apertures in said second and third tubes respectively to produce an electric signal for each passing particle the value of which is related to the dimensions of the respective particles, and processing means coupled to said scanning means and operative in response to each of said electric signals to at least count said particle passage.

20. An apparatus for studying particles of widely different sizes by use of the Coulter principle comprising,

a first vessel carrying a body of fluid having particles of widely varying size suspended therein,

at least first, second and third tubes suspended in said vessel and having first, second and third apertures respectively therein for enabling flow of fluid from said vessel to said tubes, said first and second tubes and apertures being at substantially the same depth in said vessel and said third tube and aperture being at a lower depth, said second and third apertures being substantially the same in size, and said first aperture being substantially smaller than said second and third apertures,

first, second and third fluid control means coupled to said apertures for causing said fluid to flow through said apertures,

means for actuating said second and third fluid control means for enabling flow of fluid through said second and third apertures,

first, second and third scanning means coupled to said first, second and third apertures respectively, said scanning means each being responsive to the passage of particles through said apertures to produce an electric signal for each passing particle, the value of which is related to the dimensions of respective particles,

threshold means coupled to said second scanning means and operative in response to the reduction in the repetition rate of said electric signals in excess of a particular value to develop a control signal, and

means for actuating said first fluid control means coupled to said threshold means and said first fluid control means and operative in response to said control signal to enable flow of fluid through said first aperture, and

pulse analysis means, coupled to said first and third scanning means for analyzing the electric signals produced thereby.

21. The apparatus of claim wherein said first, second and third fluid control means includes pressure differential means coupled to said first, second and third tubes for creating a pressure differential between the interior of said tubes and the interior of said vessel for allowing said fluid to flow through said apertures.

22. The apparatus of claim 21 wherein said pressure differential means includes vacuum generation means for developing a vacuum in said first, second and third tubes.

23. The apparatus of claim 20 wherein said pulse analysis means includes counter means for counting said electric signals for determining the concentration of particles in said fluid.

24. The apparatus of claim 20 wherein said means for actuating said second and third fluid control means is a switch.

25. The apparatus of claim 20 wherein said threshold means includes integration means for developing an integration voltage, said integration means being operative in response to said electric signals coupled thereto to discharge said integration voltage, and circuit means coupled to said integration means and operative in response to said integration voltage exceeding a predetermined amplitude to develop said control signal.

26. The apparatus of claim 20 wherein said first, second and third scanning means includes particle detectors of the Coulter type.

27. The apparatus of claim 20 wherein said first, second and third scanning means each includes a first electrode positioned in said vessel and in said fluid, a second electrode positioned in each one of said first, second and third tubes, a separate scanning circuit including a current source connected to each respective electrode in said tubes, and to said common electrode, the current source serving to establish a stable constricted electrical current through said respective apertures between said vessel and each of the respective tubes, for producing an electrical pulse in said scanning circuit through whose aperture a particle passes when the particle passes therethrough. 

1. A method for studying particles of widely different sizes wherein the particles are suspended in a liquid medium in a vessel and settle through the medium from top to bottom at a rate determined by their size, said method including the steps of: detecting the concentration at a particular height in said vessel of particles suspended in said liquid medium in excess of a particular size, allowing the liquid medium and particles suspended therein to pass through a first aperture in a first tube positioned at said particular height in said vessel in response to said concentration at said particular height decreasing below a first detected concentration, and allowing the liquid medium and particles suspended therein to pass into a second tube, at a second particular height on said beaker through a second aperture substantially greater in size than said first aperture.
 2. The method of claim 1 further including the steps of: detecting each particle suspended in said liquid medium passing into said first tube through said first aperture, detecting each particle suspended in said liquid medium passing into said second tube through said second aperture.
 3. The method of claim 2 wherein said step of detecting each particle passing into said first and second tubes includes the step of generating an electrical signal in response to passage through one of said first and second apertures of a particle suspended in said fluid medium, and processing said electrical signal to at least separately count said particles passing into said first and second tubes.
 4. The method of claim 3 wherein the value of said electrical signal is related to the dimensions of the particle and further including the step of processing said electrical signal to determine said dimensions.
 5. The method of claim 1 wherein said step of detecting the concentration includes, allowing the liquid medium to pass through a third aperture substantially greater in size to said first aperture, detecting particles passing through said third aperture and greater in size than said particular size, detecting a decrease in the rate of passage through said third aperture of particles in excess of said particular size.
 6. The method of claim 5 wherein the step of detecting said concentration includes the step of, generating an electrical signal in response to passage through said third aperture of a particle greater in size than said particular size, detecting the repetition rate of said electrical signals, detecting a decrease in the repetition rate of said electrical signals below a predetermined repetition rate.
 7. The method of claim 1 wherein the steps of allowing said liquid medium to pass includes the step of creating a pressure differential between said vessel and said first and second tubes for drawing said liquid through said first and second apertures.
 8. The method of claim 7 wherein said step of creating a pressure differential includes the step of creating a vacuum in said first and second tubes.
 9. An apparatus for studying particles of widely different sizes suspended in a fluid by passage of said fluid from a vessel to one of a plurality of tubes positioned in said vessel wherein each of said plurality of tubes has an aperture therein for passage of said fluid therethrough, said apparatus comprising, at least a first and second of said plurality of tubes positioned at a first height in said vessel, said first tube having a first aperture of a first particular size therein and said second tube having a second aperture of a second particular size greater than said first particular size, at least a third of said plurality of tubes at a second, lower height in said vessel, said third tube having a third aperture therein substantially larger than said first particular size of said first aperture, first control means for controlling passage of said fluid from said vessel to said first tube, first sensing means coupled to said second tube and said first control means for sensing the rate of particles entering said second tube from said vessel through said second aperture, said first sensing means operative in response to a reduction in the rate of particles in excesS of a particular size entering said second tube to actuate said control means for allowing fluid to flow from said vessel into said first tube, and second control means for controlling passage of said fluid from said vessel to said third tube.
 10. The apparatus of claim 9 further including third control means for controlling passage of said fluid from said vessel into said second tube.
 11. The apparatus of claim 9 further including second sensing means coupled to said first aperture for sensing particles entering said first tube from said vessel through said first aperture.
 12. The apparatus of claim 9 further including third sensing means coupled to said third aperture for sensing particles in said fluid entering said third tube through said third aperture from said vessel.
 13. The apparatus of claim 9 wherein said first sensing means includes first scanning means coupled to said second tube and operative in response to passage of particles in said fluid through said second aperture to produce an electric signal for each passing particle the value of which is related to the dimensions of the respective particles, and threshold means coupled to said first scanning means and operative in response to a reduction in the repetition rate of said electric signals in excess of a particular value to develop a control signal, said control means being coupled to said threshold means and operative in response to said control signal to allow fluid to flow from said vessel to said first tube.
 14. The apparatus of claim 11 wherein said second sensing means includes second scanning means coupled to said first aperture in said first tube and operative in response to passage of particles in said fluid through said first aperture to produce an electric signal for each passing particle the value of which is related to the dimensions of the respective particle, and processing means coupled to said second scanning means and operative in response to each of said electrical signals to at least count said signals for counting the number of particles passing into said first tube.
 15. The apparatus of claim 12 wherein said third sensing means includes third scanning means coupled to said third aperture in said third tube and operative in response to passage of particles in said fluid through said third aperture to produce an electric signal for each passing particle the value of which is related to the dimensions of the respective particles, and processing means coupled to said third scanning means and operative in response to said electric signals to at least count said electric signals for counting the number of particles passing into said third tube.
 16. The apparatus of claim 9 further including second control means coupled to said second tube for controlling passage of said fluid from said vessel to said second tube, and third control means coupled to said third tube for controlling passage of said fluid from said vessel to said third tube.
 17. The apparatus of claim 16 further including second sensing means coupled to said first aperture for sensing particles entering said first tube from said vessel, and third sensing means coupled to said third aperture for sensing particles entering said third tube from said vessel.
 18. The apparatus of claim 17 wherein said first sensing means includes first scanning means coupled to said second aperture in said second tube and operative in response to passage of particles through said aperture and into said second tube to produce an electric signal for each passing particle the value of which is related to the dimensions of the respective particle, and threshold means coupled to said first scanning means and operative in response to the reduction in the repetition rate of said electric signals in excess of a particular value to develop a control signal, said control means being coupled to said threshold means and operative in response to said control signal to allow fluid to flow from said vessel to said first tube.
 19. The apparatus of claim 18 wherein said second and third sensing means each include scanning means coupled to said apertures and operative in response to passage of particles through said apertures in said second and third tubes respectively to produce an electric signal for each passing particle the value of which is related to the dimensions of the respective particles, and processing means coupled to said scanning means and operative in response to each of said electric signals to at least count said particle passage.
 20. An apparatus for studying particles of widely different sizes by use of the Coulter principle comprising, a first vessel carrying a body of fluid having particles of widely varying size suspended therein, at least first, second and third tubes suspended in said vessel and having first, second and third apertures respectively therein for enabling flow of fluid from said vessel to said tubes, said first and second tubes and apertures being at substantially the same depth in said vessel and said third tube and aperture being at a lower depth, said second and third apertures being substantially the same in size, and said first aperture being substantially smaller than said second and third apertures, first, second and third fluid control means coupled to said apertures for causing said fluid to flow through said apertures, means for actuating said second and third fluid control means for enabling flow of fluid through said second and third apertures, first, second and third scanning means coupled to said first, second and third apertures respectively, said scanning means each being responsive to the passage of particles through said apertures to produce an electric signal for each passing particle, the value of which is related to the dimensions of respective particles, threshold means coupled to said second scanning means and operative in response to the reduction in the repetition rate of said electric signals in excess of a particular value to develop a control signal, and means for actuating said first fluid control means coupled to said threshold means and said first fluid control means and operative in response to said control signal to enable flow of fluid through said first aperture, and pulse analysis means, coupled to said first and third scanning means for analyzing the electric signals produced thereby.
 21. The apparatus of claim 20 wherein said first, second and third fluid control means includes pressure differential means coupled to said first, second and third tubes for creating a pressure differential between the interior of said tubes and the interior of said vessel for allowing said fluid to flow through said apertures.
 22. The apparatus of claim 21 wherein said pressure differential means includes vacuum generation means for developing a vacuum in said first, second and third tubes.
 23. The apparatus of claim 20 wherein said pulse analysis means includes counter means for counting said electric signals for determining the concentration of particles in said fluid.
 24. The apparatus of claim 20 wherein said means for actuating said second and third fluid control means is a switch.
 25. The apparatus of claim 20 wherein said threshold means includes integration means for developing an integration voltage, said integration means being operative in response to said electric signals coupled thereto to discharge said integration voltage, and circuit means coupled to said integration means and operative in response to said integration voltage exceeding a predetermined amplitude to develop said control signal.
 26. The apparatus of claim 20 wherein said first, second and third scanning means includes particle detectors of the Coulter type.
 27. The apparatus of claim 20 wherein said first, second and third scanning means each includes a first electrode positioned in said vessel and in said fluid, a second electrode positioned in each one of said first, second and third tUbes, a separate scanning circuit including a current source connected to each respective electrode in said tubes, and to said common electrode, the current source serving to establish a stable constricted electrical current through said respective apertures between said vessel and each of the respective tubes, for producing an electrical pulse in said scanning circuit through whose aperture a particle passes when the particle passes therethrough. 